1. Field of the Invention
The invention is directed to a Faraday microscope for examining specimens with stray magnetic fields in a reflected light beam path, wherein a magneto-optical film is arranged in front of the specimen and the influence of the specimen on the indicator film is evaluated with respect to optical polarization, and to a process for adjusting the Faraday microscope.
2. Background of the Invention
Arrangements of this type are known from (1) B. Ludescher, et al., "Faraday Low-Temperature Microscope for Observing Dynamic Magnetization Processes in Superconductors [Faraday-Tieftemperatur-Mikroskop zur Beobachtung dynamischer Magnetisierungsvorgange in Supraleitern]", Laser und Optoelektronik 23 (1991), pages 54-58; (2) L. A. Dorosinskii, et al., Physica C 203 (1992) , page 149; (3) M. V. Indenbohm, et al., Physica C 209 (1993), page 295.
A device for detecting magneto-optical anisotropism, particularly of magnetic recording media, is described in U.S. Pat. No. 4,410,227.
A laser polarizing microscope for observing magnetic domains is known from JP 3-185338 (A).
A Kerr microscope for examining current paths utilizing the polar Kerr effect is known from DE 4027049.
The magneto-optical Faraday effect causes a rotation of the polarization plane of polarized light at angle w as it passes through a magneto-optical material of thickness d according to the equation EQU w=RM(x)d,
where R represents a material constant of the magneto-optical material and M(x) represents the magnetization component at point x parallel to the light path.
The rotation of the plane of polarization is visible by observing the light at the polarizer-analyzer intersection. For example, with the aid of the Faraday effect, dynamic processes in superconductors and magnetic structures in magnetic storage media can be examined. In general, the constant R is so small that the Faraday effect is observed only in special materials.
A "Faraday microscope" in which a magneto-optically active film is vacuum-deposited on the superconductor to be examined is known (see 1 above). Since the Faraday rotation which can be achieved is very small, the interference between the light beams reflected at the surface of the magneto-optical film and those reflected in regions at the surface of the superconductor which are free of magnetic fields is used for evaluation. It is disadvantageous that every specimen to be analyzed must first be vacuum-deposited.
It is known (see 2, 3 above) to place thin magneto-optical indicator plates on the specimen to be analyzed, since the lateral resolution and sensitivity of the indicator decreases sharply with increasing distance from the specimen. In so doing, there is a risk that the specimen will be scratched. Moreover, a large indicator plate must be used when analyzing specimens extending over a surface area in order to avoid repeated placement. However, large indicator plates are expensive and difficult to produce. The indicator plate is formed by a substrate (garnet) on which the actual magneto-optical indicator film has been deposited. The substrate has a high index of refraction (n=approximately 2) so that the optical imaging is impaired when observing the magneto-optical indicator film.